Comparative efficacy of Knema retusa extract delivery via PEG- b-PCL, niosome, and their combination against Acanthamoeba triangularis genotype T4: characterization, inhibition, anti-adhesion, and cytotoxic activity

Background: Acanthamoeba spp. is a waterborne, opportunistic protozoan that can cause amebic keratitis and granulomatous amebic encephalitis. Knema retusa is a native tree in Malaysia, and its extracts possess a broad range of biological activities. Niosomes are non-ionic surfactant-based vesicle formations and suggest a future targeted drug delivery system. Copolymer micelle (poly(ethylene glycol)-block-poly(ɛ-caprolactone); PEG-b-PCL) is also a key constituent of niosome and supports high stability and drug efficacy. To establish Knema retusa extract (KRe) loading in diverse nanocarriers via niosome, PEG-b-PCL micelle, and their combination and to study the effect of all types of nanoparticles (NPs) on Acanthamoeba viability, adherent ability, elimination of adherence, and cytotoxicity.

Methods: In this study, we characterized niosomes, PEG-b-PCL, and their combination loaded with KRe and tested the effect of these NPs on Acanthamoeba triangularis stages. KRe-loaded PEG-b-PCL, KRe-loaded niosome, and KRe-loaded PEG-b-PCL plus niosome were synthesized and characterized regarding particle size and charge, yield, encapsulation efficiency (EE), and drug loading content (DLC). The effect of these KRe-loaded NPs on trophozoite and cystic forms of A. triangularis was assessed through assays of minimal inhibitory concentration (MIC), using trypan blue exclusion to determine the viability. The effect of KRe-loaded NPs was also determined on A. triangularis trophozoite for 24-72 h. Additionally, the anti-adhesion activity of the KRe-loaded niosome on trophozoites was also performed on a 96-well plate. Cytotoxicity activity of KRe-loaded NPs was assessed on VERO and HaCaT cells using MTT assay.

Results: KRe-loaded niosome demonstrated a higher yielded (87.93 ± 6.03%) at 286 nm UV-Vis detection and exhibited a larger size (199.3 ± 29.98 nm) and DLC (19.63 ± 1.84%) compared to KRe-loaded PEG-b-PCL (45.2 ± 10.07 nm and 2.15 ± 0.25%). The EE (%) of KRe-loaded niosome was 63.67 ± 4.04, which was significantly lower than that of the combination of PEG-b-PCL and niosome (79.67 ± 2.08). However, the particle charge of these NPs was similar (-28.2 ± 3.68 mV and -28.5 ± 4.88, respectively). Additionally, KRe-loaded niosome and KRe-loaded PEG-b-PCL plus niosome exhibited a lower MIC at 24 h (0.25 mg/mL), inhibiting 90-100% of Acanthamoeba trophozoites which lasted 72 h. KRe-loaded niosome affected adherence by around 40-60% at 0.125-0.25 mg/mL and removed Acanthamoeba adhesion on the surface by about 90% at 0.5 mg/mL. Cell viability of VERO and HaCaT cells treated with 0.125 mg/mL of KRe-loaded niosome and KRe-loaded PEG-b-PCL plus niosome exceeded 80%.

Conclusion: Indeed, niosome and niosome plus PEG-b-PCL were suitable nanocarrier-loaded KRe, and they had a greater nanoparticle property to test with high activities against A. triangularis on the reduction of adherence ability and demonstration of its low toxicity to VERO and HaCaT cells.